This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-181601 now Japanese Patent 2001-013392, filed Jun. 28, 1999; and No. 11-181602 now Japanese Patent 2001-013390, filed Jun. 28, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to an optical element and in particular, to a lens shape and a lens frame for retaining the lens.
When a plurality of lenses are arranged in a cylindrical lens barrel using a lens frame, the performance of this lens optical system heavily depends on a designed centering accuracy for the lens and the lens frame and a positioning accuracy with which these lenses are supported and fixed via the lens frame in such a manner that each lens is centered on an optical axis.
With respect to techniques for optical lenses, an approach for mounting the lenses in the lens barrel with a resin while aligning them on the optical axis using, for example, the xe2x80x9cbell chuck methodxe2x80x9d has been proposed in Jpn. Pat. Appln. KOKAI Publication No. 59-68710 as an example of a method for assembling a lens system.
In addition, techniques for improving the surface shape of the lenses and applying a frame member that contacts with the lens surfaces include a lens retaining mechanism such as that disclosed in Jpn. Pat. Appln. KOKAI Publication No. 58-158615, which is one of retaining techniques for reducing aberrations resulting from inclination of the lenses with respect to the optical axis.
These conventional techniques improve the lenses or the lens frame in order to correctly position the lenses.
The above described improvements can simplify or omit a lens xe2x80x9ccenteringxe2x80x9d step to improve an assembly operation or optical performance to some degree. To correctly position the lens on the lens frame, however, the assembly method in Jpn. Pat. Appln. KOKAI Publication No. 59-68710 provides a radial gap in an inner diameter of the lens frame so as to enable adjustments called xe2x80x9calignmentsxe2x80x9d while supporting the lens on its predetermined spherical surface based on, for example, the bell chuck method. Accordingly, the lens may shift within a range corresponding to the predetermined amount of backlash (fitting backlash), so that shifting of the spherical surface, which is in abutment with the lens frame, may degrade the performance of the optical system.
The lens retention mechanism disclosed in Jpn. Pat. Appln. KOKAI Publication No. 58-158615 may cause what is called xe2x80x9cparallel decenteringxe2x80x9d in a direction orthogonal with the optical axis. This lens decentering may also degrading the performance of the optical system.
Thus, the prior art has disclosed no techniques for initial positioning or maintenance of initial positioning accuracy or easy positioning techniques that can be achieved while maintaining a designed accuracy.
Many typical lenses are supported at their peripheral or spherical surface. If, however, a lens, comprising a plurality of spherical surfaces, is supported at part of its optical characteristic surface (for example, an end surface of the lens close to its periphery), then in order to enhance a mounting accuracy for a main optical characteristic surface (a first spherical surface) that is important in terms of performance, improvements are required to prevent the first spherical surface from shifting from the optical axis even if a supported position on the supported surface is displaced by a certain amount within this surface.
It is thus an object of the present invention to provide a support structure comprising a lens and a lens frame and which provides fitting backlash between the lens and the lens frame to enable positioning while restraining degradation of optical performance even if the lens shifts.
To solve the above described problems to attain the object, the present invention provides the following means:
According to the present invention, if a lens is supported at its end surface close to its periphery which is adjacent to its optical characteristic surface constituting, for example, a spherical surface, then in order to enhance a mounting accuracy for a main optical characteristic surface (a first spherical surface), the lens is shaped to be supported at a spherical surface having the same center as the first spherical surface (the center of the first spherical surface is hereafter simply referred to as the xe2x80x9ccenterxe2x80x9d), that is, at a xe2x80x9cconcentric spherical surfacexe2x80x9d.
For example, a first invention provides a lens comprising two opposed optical characteristic surfaces, wherein one of the two optical characteristic surfaces is formed, for example, of a spherical surface, while the other has a spherical surface annularly formed in a peripheral portion thereof and having the same center as the first optical characteristic surface.
This invention also proposes a lens having its center on an optical axis and comprising two spherical surfaces, wherein one of the spherical surfaces comprises a spherical surface annularly formed in a peripheral portion thereof and having the same center as the other spherical surface.
This invention also proposes a lens comprising a first optical characteristic surface, a second optical characteristic surface including a spherical surface opposed to the first optical characteristic surface, and a spherical portion formed contiguously to the first optical characteristic surface in a surrounding fashion and having the same spherical center as the second optical characteristic surface.
In addition, according to this invention, if a lens is supported inside a lens frame comprising, for example, a spherical surface, then in order to improve a mounting accuracy for a main optical characteristic surface (a first spherical surface or a second spherical surface) of the lens, the lens frame is shaped so as to be coaxially supported by having the same center as the first spherical surface or the second spherical surface.
For example, a second invention proposes a lens frame wherein a surface for receiving a lens for support and retention is spherical.
This invention also proposes a lens frame comprising a frame member having a spherical shape for receiving one of two opposed spherical surfaces of a lens to support and retain the lens.
This invention also proposes a lens frame comprising, to support a circular lens with two opposed spherical surfaces, an annular frame member using as a lens receiving surface a spherical surface that receives one of the spherical surfaces of the lens and that has the same center as the other spherical surface.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.